1. Field of the Invention
The present invention relates to a method of producing D-psicose crystals from a D-psicose solution by using supersaturation.
2. Description of the Related Art
D-psicose is a natural sugar present in a trace amount in isomerization of molasses or glucose and a monosaccharide with a sweetness of about 70% relative to sugar. It has been reported that D-psicose is a sweetener that has little effect on body weight increase because it is not metabolized by humans, has substantially no calories, and inhibits the formation of body fat (Matuo, T. et. Al., Asia Pac. J. Clin. Nutr., 10, 233-237, 2001; Matsuo, T. and K. Izumori, Asia Pac. J. Clin. Nutr., 13, S127, 2004).
Recently, effects of D-psicose on non-carious and anti-carious functions have been reported, and thus development of D-psicose, as a material which aids in teeth health and as a sweetener which may replace sugar, has been actively performed.
Although D-psicose has attracted attention from the food industry as a sweetener to prevent an increase in body weight due to its properties and functionalities, only a trace amount of D-psicose is produced from fructose at high temperatures, and thus it is difficult to produce D-psicose via chemical synthesis. Although mass production methods by reacting fructose with D-tagatose epimerase or reacting fructose with D-psicose epimerase have been reported, the yields of D-psicose are so low that production costs thereof are high.
Recently, the present inventors have reported a method of economically producing D-psicose by isomerizing glucose to fructose, followed by a reaction of fructose with immobilized cells which produces D-psicose epimerase (Korea Patent Application No. 10-2009-0118465).
Reaction solutions containing D-psicose produced by enzymatic reactions are low-purity products that contain D-psicose in solid form in an amount of about 20% to about 30% by weight, and thus it is required to isolate D-psicose at high purity. Various methods are applied to materials that are industrially produced to isolate them at high purity. In the case of sugars, chromatography is usually used to prepare a highly pure liquid, followed by crystallization to obtain high-purity sugar product. For D-psicose, an industrially applicable method of production is yet to be developed.
A method of preparing D-psicose in a powder form by removing unreacted fructose in a D-psicose reaction solution via yeast fermentation and using a large amount of ethanol was reported (Kei T. et. al., J. Biosci. Bioeng., 90(4), 453-455, 2000). However, the use of ethanol in large amounts requires expensive facilities for explosion proofness and recovery of products, and problems, such as stirrer failure caused by the use of organic solvents and presence of foreign materials in recovered products, can occur. In addition, because the final products are in the form of fine powders, they may be lost in large quantities during dehydration, washing, and drying processes. While D-psicose is powdered to produce final products, the powders are adsorbed to each other, which introduces impurities among the powder particles, thereby lowering the purity of the final product. For the products in the form of fine powders, the increase in volume is larger than the increase in weigh, which leads to increase in manufacturing costs due to high volume packaging and additional costs in the distribution. In addition, such products in fine chemicals are disadvantageous in food manufacturing process due to low flowability. Therefore, there still remains a need for a method of producing pure D-psicose, in the form of crystals rather than fine powders, in order to economically produce D-psicose without using organic solvents such as ethanol and improve flowability in the manufacturing process and product value.